1. Field of the Invention
The present invention relates to an occupant detection system for detecting an occupant on a vehicle seat and a method of determining the occupant.
2. Description of Related Art
An air-bag device is mounted in a vehicle in order to reduce damage to an occupant when the vehicle collides with an object such as another vehicle. The air-bag device is provided in a passenger seat in addition to a driver seat. The air-bag device is actuated, when a calculating unit of the air-bag device determines that the vehicle collides with the object. The calculating unit performs calculations based on signals output from a sensor, e.g., acceleration sensor, on the vehicle.
The air-bag device is set to be actuated, whenever the vehicle collides with the object, even if any occupant is not seated on the passenger seat. However, the air-bag device is not to be actuated, when a body size of the occupant is small. An adult can be protected by the air-bag device, when the vehicle collides with the object. In contrast, for example, a child may not be protected by the air-bag device, and rather a head of the child may be damaged by the air-bag device, because the head of the child is positioned lower than that of the adult.
In order to determine whether the occupant is an adult or not, an occupant detection system having an occupant detection sensor is provided on the passenger seat. For example, Japanese Patent No. 3346464 discloses an occupant detection system for detecting an occupant and its seating state. The occupant detection system includes plural pairs of antenna electrodes in the passenger seat, so that one of the pairs of antenna electrodes can detect the occupant.
However, if the passenger seat is wet, detection accuracy of the system may be lowered. In this case, because whole wet part operates as an antenna, an erroneous output larger than a correct output may be output. Thus, the system may determine the occupant to be an adult, while the occupant is a child. As a result, the air-bag device may be erroneously actuated.
In contrast, U.S. Pat. No. 6,816,077 (corresponding to JP-A-2002-347498) discloses an occupant detection system having a moisture sensor in a seat. This system can have high detection accuracy, because erroneous detections due to moisture in the seat can be reduced. However, the moisture sensor causes an increase in its product cost.
Moreover, US 2005/0128082 A1 (corresponding to JP-A-2003-504624) discloses an occupant-detecting device including an electric field sensor and a detection circuit. The detection circuit applies vibration signals to an electric field such that the vibration signals are most weakly affected by moisture in a seat. However, affects caused by the moisture cannot completely be eliminated.